A high voltage DC power supply system is required for driving an electric machine that incorporates a high voltage electrical drive motor and electric auxiliaries. The integrity of the high voltage system is critical to the reliability of the machine. Typically, the machine frame is electrically insulated from the terminals or conductors of the high voltage power supply. Under normal working conditions, DC leakage currents on the order of microamps exist between the conductors of the high voltage power supply and the machine frame. Thus, the leakage resistances between the conductors of the high voltage power supply and the frame are normally very high. However, under faulty conditions (e.g., insulation failure), electric currents from a high voltage power supply may leak to a machine frame. Such leakage currents, when significant, may be an indication of machine component fatigue or failure of a conductor's insulation. In order to ensure the proper operating conditions and the integrity of the machines, it is necessary to detect electrical leakage between the conductors of the high voltage power supply and the machine frame. High voltage systems typically include a ground fault detection system to ensure proper operating conditions.
Since ground fault detection systems are essential for protecting equipment, proper testing of the detection systems is crucial. Typically, specialized personnel (not a machine operator) test ground fault detection systems of a machine as part of a scheduled maintenance plan. This testing involves connecting external testing units directly to the ground fault detection system of a machine and simulating an electrical leakage. There are two significant problems with this testing regime. First, the testing method requires the machine to be out-of-service even if no fault is found with the ground fault detection system. More significantly, the ground fault system may not be functioning correctly for an extended period (between service intervals), which may increase the occurrence of a machine malfunctioning without an alarm. A second problem is that operators lack a field method, test equipment, and specialized training for quickly and efficiently ensuring proper operating conditions. For example, if operators observe an actual field condition that they believe might compromise the ground detection system (e.g. the insulation is cracked on an electrical connector), the operators must either incur a costly delay waiting to have the machine serviced or effect repairs themselves, possibly insufficiently.
One grounding system test apparatus is disclosed in U.S. Pat. No. 4,609,865 (the '865 patent) issued to Goodman et al. on Sep. 2, 1986. The '865 patent discloses an apparatus that is mounted in or alongside a conventional power center or distribution box in a power system located in a coal mine or similar location. The apparatus introduces a test current into the power system. The apparatus includes a means for adjusting the test current through an adjustable resistor to a predetermined value to check the tripping values of ground fault relays.
Though introducing an actual leakage into a power system to verify actual operation of a ground fault detection system, the '865 patent fails to provide a quick and efficient method for individual operators to instantaneously check the operating condition of machines. The '865 patent also fails to provide a testing method that is applicable at both a low operating voltage and a high operating voltage.
The testing system and method of the present disclosure solve one or more of the problems set forth above.